1. Field of the Invention
The present invention relates to an apparatus and method for non-destructive testing of primers. More particularly, the present invention relates to an apparatus and method for non-destructive testing of a subassembly of a vehicle that includes an ignitor for activating an airbag or a belt tightener.
2. Description of the Related Art
An ignitor is an ignition element in the form of a resistance heating element or a resistance wire used to activate an airbag or a belt tightener, for example. To activate the ignitor, an electrical current is applied to the ignitor. The electrical energy supplied is converted by the ignitor into thermal energy, which in turn is supplied to a gas generator coupled to the ignitor. The gas generator then releases the gas bound in tablet form to inflate, for example, an airbag.
The service readiness of a safety-related subassembly, or the ignitor integrated therein can be tested by measuring the ohmic resistance of the ignitor. If, for example, the measured electrical resistance is too high, this may indicates an interruption in the triggering circuit or an incorrectly installed part and thus, a non-functioning airbag or belt tightener. If, on the other hand, the resistance measured is too low, this may indicate a short circuit in the ignitor/cabling. In this case, the control circuit cannot generate enough power to activate the ignitor. A service-ready ignition element is determined when the measured resistance of the ignitor falls within a range specified by the manufacturer.
German Publication DE 199 00 978 C2 discloses a circuit arrangement in which a test current is fed into the ignitor to determine the resistance of the ignitor. Using a current mirror circuit, the test current flowing through the ignitor is applied to a measuring resistance. Finally, the voltage drop at the measuring resistance can be used to infer the magnitude of the ohmic resistance of the ignitor.